1. Field of the Invention
This invention relates generally to a method of indirectly measuring the concentrations of carbon dioxide in the oceans, and more specifically to a robotic device which can operate autonomously in the oceans for extended periods of time, while recording carbon sediment flux at resolution times of minutes or hours over months to years.
2. Background of the Related Art
With the increasing concerns about climate change, and the role that the observed concentrations of carbon dioxide plays in this change, there is increasing interest in better understanding the carbon dioxide cycle with its interactions over land and sea. Because of the ease of accessibility, it is relatively easy to monitor the generation and discharge of CO2 into the atmosphere. It is also reasonably possible to predict the capacity for land based plant matter using such processes as photosynthesis to convert atmospheric CO2.
The atmospheric carbon inventory gains due to anthropogenic emissions are lower than expected because CO2 is being taken up by land ecosystems and by the ocean. It has been estimated that about half of the carbon dioxide sink from the atmosphere is absorbed over land, and the other half absorbed over the oceans. This will change in the future.
Carbon dioxide once absorbed by the ocean waters, in its dissolved form is chemically converted into biomass by ocean going plant life such as plankton (under the influence of sunlight) which presently account for half of global photosynthesis. The absorption of extra CO2 into the ocean causes acidification of surface waters and the impact on ocean photosynthesis is poorly understood.
Typically such biomass as it decays, and/or is consumed by aquatic life forms is converted into particulate organic carbon debris (POC) or sediment. The amount of generated sediment or detritus is a complex function of existing biomass. Some species of phytoplankton (such as coccolithophorids) also convert dissolved inorganic carbon during photosynthesis (biologic processes) into particulate inorganic carbon (PIC), which can take the form of biogenic particles of calcium carbonate (CaCO3). This PIC component occurs as both calcite and aragonite mineral polymorphs of CaCO3 in marine environments, ranging in concentration form less than 0.01 micromoles/liter in deep ocean waters to over 30 micromoles per liter in open ocean surface waters during phytoplankton blooms. Some zooplankton (i.e., Pteropods, Foraminifera) also make shells composed of calcite and aragonite. Coral reefs are also formed of aragonite. Acidification of seawater due to human generated CO2 is believed to negatively impact both calcifying phytoplankton and zooplankton.
Despite the important role that the oceans play in the global carbon cycle and of the regulation of levels of atmospheric CO2, the biological and physical processes that sequester carbon remain poorly understood. This is due in large part because of the difficulties of making continuous observations in the vast waters of the world's oceans, including those areas of extreme weather, ice, winds and the like. Yet, the upper kilometers of the ocean are both biologically quite active, and very observation-poor.
To date, most such CO2 monitoring has been ship based, with sampling units placed at sea and ship tenders required to be in position to take periodic readings. Conventional ship based sampling methods such as the collecting of particles by filtration using rosette-mounted bottles or large volume in situ filtration cannot adequately capture the spatial and temporal variability of biomass material in the ocean. Further, such ship based tender is time consuming, and expensive, and this thus severely limits the number of sampling stations which can be established. Accordingly, there is a need for the development of an autonomous, robotic platform for real time monitoring of the biotic carbon flux on a continuous basis, a monitor which may be placed in an ocean environment and data collected for days, months and even years at a time without special tending, where data can be relayed in real time via satellite.